1. Field of the Invention
The present invention relates to a chin position calculating process. Particularly, the present invention relates to a chin position calculating apparatus suited for automatically detecting the positions of the chins of humans in digital images, an image processing apparatus that employs the chin position calculating apparatus, a chin position calculating method, and a recording medium having a chin position calculating program recorded therein.
2. Description of the Related Art
Image processes, such as color tone correction, brightness correction, and image synthesis, have become easy to administer on digital images obtained by photography using digital still cameras, when photographing portraits of people. Therefore, various image processes are administered on photographed digital images such that they have favorable finishes, then the digital images are printed out.
There are empirically determined preferred compositions for portraits. When people are the subjects of photography, photography is performed with the faces of the people as reference points for compositional balance such that such compositions are achieved. However, photography having ideal compositions cannot always be performed. Therefore, faces are automatically detected from within digital images which have been photographed with compositions that are not ideal, the images are trimmed with the detected faces as reference points for compositional balance, then the trimmed images are printed out, such that the images achieve ideal compositions. However, there is a problem that optimal trimming processes cannot be administered unless the tops of heads and chins are accurately detected.
For this reason, methods for accurately detecting the positions of chins band methods for trimming images using data regarding detected chin positions have been proposed. For example, Japanese Unexamined Patent Publication No. 2005-202841 discloses a method, in which: outlines of faces included in images are extracted; and quadratic curves that are convex toward the downward direction and which are similar to the outlines of chins are obtained; to calculate the positions of chins. Japanese Unexamined Patent Publication No. 2000-036032 discloses a method, in which: differences between background images and images of subjects are obtained; mask images of humans are generated from the images of the subjects; and trimming processes are administered by searching for the positions of the tops of heads and chins from within the mask images, such that the faces of the subject are at predetermined positions. Japanese Unexamined Patent Publication No. 2007-072628 discloses a method in which: edge processes are administered on images that represent faces; and each pixel value obtained by the edge processes is projected in a predetermined direction to generate histograms; to estimate the positions of chins. U.S. Pat. No. 7,324,669 discloses a method for trimming images, in which: faces included in images are extracted; and the positions of chins are calculated, based on the presumption that the ratio of distances between chins and mouths and distances between eyes and mouths are constant.
However, there are various problems with the aforementioned image processing methods for detecting the chin positions, as will be described below. In the method disclosed by Japanese Unexamined Patent Publication No. 2005-202841, there are cases in which the shapes of chins differ if faces are not facing front, and also due to differences among individuals. Therefore, the shapes of chins do not necessarily approximate a downwardly convex quadratic curve, and erroneous detection may occur. In the method disclosed by Japanese Unexamined Patent Publication No. 2000-036032, there are cases in which borderlines between the outlines of faces and necks cannot be continuously recognized, due to intensities of illuminating light sources and skin tone. In these cases, stable performance cannot be obtained in the extraction process using mask images. In the method disclosed by U.S. Pat. No. 7,324,669, there are cases in which erroneous detection may occur, due to some people not having the same ratio of distances between chins and mouths and distances between eyes and mouths as the accepted standard.